1. Introduction

Hue is a graphical user interface to operate and develop applications for
Apache Hadoop. Hue applications are collected into a desktop-style environment
and delivered as a Web application, requiring no additional installation for
individual users.

This guide describes how to install and configure a Hue tarball. For
information about installing Hue packages, see
Installing Hue.

There is also a companion SDK guide that describes how to develop
new Hue applications:
Hue SDK Documentation

2.1. Install Hadoop from CDH3

To use Hue, you must install and run Hadoop from CDH3 Beta 4 or later. If you
are not running this version of CDH or later, upgrade your cluster before
proceeding.

2.2. Install Hue

Hue consists of a web service that runs on a special node in your cluster.
Choose one node where you want to run Hue. This guide refers to that node as
the Hue Server. For optimal performance, this should be one of the nodes
within your cluster, though it can be a remote node as long as there are no
overly restrictive firewalls. For small clusters of less than 10 nodes,
you can use your existing master node as the Hue Server.

You can install Hue anywhere on your system - it does not need root permission
although additional third-party SDK applications may.
It is a good practice to create a new user for Hue and either install Hue in
that user’s home directory, or in a directory within /usr/local.

2.2.3. Install Hadoop Plugins

In order to communicate with Hadoop, Hue requires a plugin jar that you must
install and configure. This jar is:

desktop/libs/hadoop/java-lib/hue-plugins-*.jar

relative to the Hue installation directory.

Run these commands to create a symlink your Hadoop lib directory
(/usr/lib/hadoop-0.20/lib if you installed CDH via a Debian or RPM package)
to this jar:

2.2.5. Starting Hue

To start Hue, use build/env/bin/supervisor. This will start
several subprocesses, corresponding to the different Hue components.

2.2.6. Troubleshooting the Hue Tarball Installation

Q: I moved my Hue installation from one directory to another and now Hue no. longer functions correctly.

A: Due to the use of absolute paths by some Python packages, you must run a
series of commands if you move your Hue installation. In the new location, run:

$ rm app.reg
$ rm -r build
$ make apps

Q: Why does "make install" compile other pieces of software? A: In order to ensure that Hue is stable on a variety of distributions and
architectures, it installs a Python virtual environment which includes its
dependencies. This ensures that the software can depend on specific versions
of various Python libraries and you don’t have to be concerned about missing
software components.

2.3. Configuring Hadoop for Hue

Hue requires that you install and configure some plugins in your
Hadoop installation. In order to enable the plugins, you must make some
small additions to your configuration files. Make these configuration changes
on each node in your cluster by editing the following files
in: /etc/hadoop-0.20/conf/

2.4. Further Hadoop Configuration and Caveats

2.4.1. HADOOP_CLASSPATH Caveat

If you are setting $HADOOP_CLASSPATH in your hadoop-env.sh, be sure
to set it in such a way that user-specified options are preserved. For example:

Correct:

# HADOOP_CLASSPATH=<your_additions>:$HADOOP_CLASSPATH

Incorrect:

# HADOOP_CLASSPATH=<your_additions>

This enables certain components of Hue to add to
Hadoop’s classpath using the environment variable.

2.4.2. hadoop.tmp.dir

If your users are likely to be submitting jobs both using Hue and from the
same machine via the command line interface, they will be doing so as the hue
user if they’re using Hue and via their own user account on the command line.
This leads to some contention on the directory specified by hadoop.tmp.dir,
which defaults to /tmp/hadoop-${user.name}. Specifically, hadoop.tmp.dir
is used to unpack jars in bin/hadoop jar. One work around to this is
to set hadoop.tmp.dir to /tmp/hadoop-${user.name}-${hue.suffix} in the
core-site.xml file:

Unfortunately, when the variable is unset, you’ll end up
with directories named /tmp/hadoop-user_name-${hue.suffix} in
/tmp. The job submission daemon, however, will still work.

The Beeswax server writes into a local directory on the Hue machine
that is specified by hadoop.tmp.dir to unpack its jars. That directory
needs to be writable by the hue user, which is the default user who starts
Beeswax Server, or else Beeswax server will not start. You may also make that
directory world-writable.

2.5. Restart Your Hadoop Cluster

Restart all of the daemons in your cluster so that the plugins can be loaded.

You can confirm that the plugins are running correctly by tailing the daemon
logs:

Hue currently requires that the machines within your cluster can connect to
each other freely over TCP. The machines outside your cluster must be able to
open TCP port 8088 on the Hue Server to interact with the system.

3. Configuring Hue

Hue ships with a default configuration that will work for
pseudo-distributed clusters. If you are running on a real cluster, you must
make a few changes to the /etc/hue/hue.ini configuration file. The
following sections describe the key configuration options you must make to
configure Hue.

Listing all Configuration Options

To list all available configuration options, run:

/usr/share/hue/build/env/bin/hue config_help | less

This commands outlines the various sections and options in the configuration,
and provides help and information on the default values.

Viewing Current Configuration Options

To view the current configuration from within Hue, open:

http://<hue>/dump_config

Using Multiple Files to Store Your Configuration

Hue loads and merges all of the files with extension .ini
located in the /etc/hue/conf/ directory. Files that are alphabetically later
take precedence.

3.1. Web Server Configuration

Hue uses the CherryPy web server. You can use the following options to
change the IP address and port that the web server listens on. The default
setting is port 8088 on all configured IP addresses.

# Webserver listens on this address and port
http_host=0.0.0.0
http_port=8088

3.1.1. Specifying the Secret Key

For security, you should also specify the secret key that is used for secure
hashing in the session store.

Open the /etc/hue/hue.ini configuration file. In the desktop section, enter
a long series of random characters (30 to 60 characters is recommended).

If you don’t specify a secret key, your session cookies will not be
secure. Hue will run but it will also display error messages telling you to
set the secret key.

3.2. Authentication

By default, the first user who logs in to Hue can choose any
username and password and becomes an administrator automatically. This
user can create other user and administrator accounts. User information is
stored in the Django database in the Django backend.

To upload files using the Hue File Browser over HTTPS requires
using a proper SSL Certificate. Self-signed certificates don’t
work.

3.4. Pointing Hue to Your Master Nodes

If your Hadoop cluster contains multiple nodes, you should configure
Hue to point to the external hostnames of your NameNode and
JobTracker. To do so, change the namenode_host and jobtracker_host
lines in the /etc/hue/hue.ini configuration file. Refer to the inline comments
in the configuration file for more information.

4. Starting Hue from the Tarball

After your cluster is running with the plugins enabled, you can start Hue on
your Hue Server by running:

# build/env/bin/supervisor

Your Hue installation is now running.

5. Administering Hue

Now that you’ve installed and started Hue, you can feel free to skip ahead
to the Using Hue section. Administrators may want to refer to this
section for more details about managing and operating a Hue installation.

5.1. Hue Processes

5.1.1. Process Hierarchy

A script called supervisor manages all Hue processes. The supervisor is a
watchdog process — its only purpose is to spawn and monitor other processes.
A standard Hue installation starts and monitors the following processes:

runcpserver - a web server based on CherryPy that provides the core web
functionality of Hue

jobsubd - a daemon which handles submission of jobs to Hadoop

beeswax server - a daemon that manages concurrent Hive queries

If you have installed other applications into your Hue instance, you may see
other daemons running under the supervisor as well.

You can see the supervised processes running in the output of ps -f -u hue:

Note that the supervisor automatically restarts these processes if they fail for
any reason. If the processes fail repeatedly within a short time, the supervisor
itself shuts down.

5.2. Hue Logging

The Hue logs are found in /var/log/hue. Inside the log directory you can find:

An access.log file, which contains a log for all requests against the Hue
web server.

A supervisor.log file, which contains log information for the supervisor
process.

A supervisor.out file, which contains the stdout and stderr for the
supervisor process.

A .log file for each supervised process described above, which contains
the logs for that process.

A .out file for each supervised process described above, which contains
the stdout and stderr for that process.

If users on your cluster have problems running Hue, you can often find error
messages in these log files. If you are unable to start Hue from the init
script, the supervisor.log log file can often contain clues.

5.2.1. Viewing Recent Log Messages through your Web Browser

In addition to logging INFO level messages to the logs directory, the Hue
web server keeps a small buffer of log messages at all levels in memory. You can
view these logs by visiting http://myserver:8088/logs. The DEBUG level
messages shown can sometimes be helpful in troubleshooting issues.

5.3. The Hue Database

Hue requires a SQL database to store small amounts of data, including user
account information as well as history of job submissions and Hive queries.
By default, Hue is configured to use the embedded database SQLite for this
purpose, and should require no configuration or management by the administrator.
However, MySQL is the recommended database to use; this section contains
instructions for configuring Hue to access MySQL and other databases.

5.3.1. Inspecting the Hue Database

The default SQLite database used by Hue is located in:

`/usr/share/hue/desktop/desktop.db`.

You can inspect this database from the command line using the sqlite3
program. For example:

It is strongly recommended that you avoid making any modifications to the
database directly using SQLite, though this trick can be useful for management
or troubleshooting.

5.3.2. Backing up the Hue Database

If you use the default SQLite database, then copy the desktop.db file to
another node for backup. It is recommended that you back it up on a regular
schedule, and also that you back it up before any upgrade to a new version of
Hue.

5.3.3. Configuring Hue to Access Another Database

Although SQLite is the default database type, some advanced users may prefer
to have Hue access an alternate database type. Note that if you elect to
configure Hue to use an external database, upgrades may require more manual
steps in the future.

The following instructions are for MySQL, though you can also configure Hue to
work with other common databases such as PostgreSQL and Oracle.

Tested Database Backends

Note that Hue has only been tested with SQLite and MySQL database backends.

5.3.3.1. Configuring Hue to Store Data in MySQL

To configure Hue to store data in MySQL:

Create a new database in MySQL and grant privileges to a Hue user to manage
this database.

Your system is now configured and you can start the Hue server as normal.

6. Hue Applications

This section includes documentation specific to built-in Hue applications.

6.1. Beeswax, the Hive UI

6.1.1. Introduction

Beeswax is an application that is a component within Hue that helps you use
Hive to query your data.

6.1.2. Installation

Beeswax is installed as part of Hue.

6.1.3. Hive Configuration

Beeswax, the Hive interface in Hue, includes Hive 0.7. You do
not need an existing Hive installation.

Your Hive data is stored in HDFS, normally under /user/hive/warehouse
(or any path you specify as hive.metastore.warehouse.dir in your
hive-site.xml). Make sure this location exists and is writable by
the users whom you expect to be creating tables. /tmp (on the local file
system) must be world-writable, as Hive makes extensive use of it.

If you used the embedded Hive MetaStore functionality of Beeswax in Hue from
versions prior to Hue 1.2, read this section. Hue 1.2 includes changes in the
Hive MetaStore schema that are part of the Hive 0.7 release. If you want to use
Beeswax in Hue 1.2, it is imperative that you upgrade the Hive MetaStore schema
by running the appropriate schema upgrade script located in the
apps/beeswax/hive/scripts/metastore/upgrade directory in the Hue installation.
Scripts for Derby and MySQL databases are available. If you are using a
different database for your MetaStore, you will need to provide your own
upgrade script.

6.1.4. Configuration

6.1.4.1. No Existing Hive Installation

Familiarize yourself with the configuration options in
hive-site.xml (see
http://wiki.apache.org/hadoop/Hive/AdminManual/Configuration).
Having a hive-site.xml is optional but often useful, particularly on setting
up a metastore.
You may store the hive-site.xml in /etc/hue/conf, or instruct
Beeswax to locate it using the hive_conf_dir configuration variable. See
/etc/hue/conf/hue-beeswax.ini.

6.1.4.2. Existing Hive Installation

In /etc/hue/conf/hue-beeswax.ini, modify hive_conf_dir to point to the
directory containing hive-site.xml.

7. Using Hue

After installation, you can use Hue by navigating to http://myserver:8088/.
The following login screen appears:

Launch applications on the bottom-right.

The Help application guides users through the various installed applications.

7.1. Supported Browsers

Hue is primarily tested on Firefox 3.5 and Firefox 3.6, on Windows, Mac, and
Linux. Google Chrome and Safari work as well.

7.2. Feedback

7.3. Reporting Bugs

If you find that something doesn’t work, it’ll often be helpful to include logs
from your server. These are available at the /logs URL on Hue’s web server
(not part of the graphical Hue UI). Please download the logs as a zip (or cut
and paste the ones that look relevant) and send those with your bug reports.